Используйте «armhole» в предложении

1. He folded this strip in two, took off his wide, strong summer overcoat of some stout cotton material (his only outer garment) and began sewing the two ends of the rag on the inside, under the left armhole

2. "How could I go to sleep again with nothing done? Yes, yes; I have not taken the loop off the armhole! I forgot it, forgot a thing like that!